Back in June, Mazda spokesperson Beverly Braga told us that "Mazda remains committed to bringing the Skyactiv-D clean diesel technology to North America", though there is no set date until "the final product meets [Mazda's] expectations."

The decision to make a diesel-hybrid is an unusual one for Mazda--the company has previously been dismissive of hybrid vehicle technology, putting its faith into ever-improving gasoline engines. More recently, Mazda changed its tune--announcing a hybrid version of the Mazda3 compact, also for Japan.

The diesel-hybrid is likely to use a fairly simple setup, with electric power providing assistance to the diesel engine--but it could prove highly efficient.

On the city-focused Japanese test cycle, the Mazda hints the new car could achieve up to 95 miles per gallon.

While that has absolutely no parity with the EPA standard used in the U.S, a better metric is the eight percent better economy promised over the Toyota Prius C, badged Aqua in Japan. That equates to a combined figure around the 54 mpg mark.

Japan, traditionally skeptical of diesel vehicles given its crowded city streets, has seen huge increases in diesel sales in recent years: last year's tally of 76,000 vehicles was 1.9 times greater than 2012's diesel sales.

Diesel hybrid models are notable by their relative absence both in the U.S. and even in the pro-diesel European market.

The French and Swedish makes use a through-the-road setup with electric power to the rear wheels alone, while Mercedes uses a more traditional setup, slotting an electric motor between engine and gearbox to provide electric assistance.

While the economy benefits are potentially great, weight, cost and complication all increase, and the benefits rarely offset the initial price paid by the customer.

If Mazda can price its diesel-hybrids competitively, it could be onto a winner. Whether the car will ever hit the American market may depend on whether the regular diesel ever precedes it...